The present invention relates to an involute gearset, which formed by meshing gear teeth of at least two gear wheels of a gear mechanism, with each gear tooth having a tooth profile formed of different profile shapes.
The concept gearwheel mechanism covers gear pumps as well as gear type motors, which includes at least a pair of gear wheels in engagement with one another. Both meshing gear wheels can have an external set of teeth as well as an internal set of teeth. In the last-named embodiment a spur gear wheel provided with external teeth and designated as external wheel meshes with a gear wheel carrying internal gearing designated as a ring gear.
In gearwheel mechanisms of the type under discussion here it has often proved to be disadvantageous, that considerable noise arises in operation, which among other reasons is caused by a so-called entry shock. Such shocks arise always if a new tooth of a gear wheel enters into engagement with the tooth flank of the associated second gear wheel. An entry shock is for instance caused by pitch deviation, which is based either on fabrication processes or on a deformation of the teeth meshing with each other. Thus deformations based upon flexing of the teeth under load are practically unavoidable in the operation of a gearwheel mechanism. Also in those cases when fabrication errors are reduced to a minimum, engagement interference caused by deformations under load can occur in the course of lagging of the driven gear wheel, with the engagement interference resulting in an engagement shock.
It is therefore the task of the invention to provide a gear of a gearwheel mechanism or geared machine of the above-mentioned type, where the noise generation is considerably reduced.
The task of the invention is achieved by providing an involute gearset, in which the tooth flanks of the individual teeth of the gear wheels comprise an involute in the flank central region adjoined by an arcuate region which passes tangentially into a straight line segment intersecting the tooth end face, so that a straight line of action is formed at the pitch point in the involute region.
Proceeding from the conventional involute gearing, it is contemplated a form the tooth profiles or flanks of the wheels meshing with one another of differently curved segments and thereby create a so-called cycloid gearing. The conventional involute is provided in the central region of the tooth profile or flank which continues in an arcuate region towards the tip area of the tooth with the arcuate segment transiting tangentially into an adjacent straight line segment. This straight line segment cuts then directly through the tip surface of the tooth. In this way a straight line of action is assured at the pitch or rolling point in the region of the involute. Engagement shocks can be avoided due to the design of the tooth flanks of the teeth in operation of the gearwheel mechanism, also in case of fabrication flaws or by deformation under load of the individual teeth meshing with each other. This results in an operation of the mechanism generating very little noise.
An embodiment form of the gearwheel mechanism is especially preferred where the arcuate region is shaped as a circular arc, whose radius of curvature coincides with the radius of curvature of the involute region directed adjacent to the arcuate region, wherein preferably the involute and the arcuate region transit tangentially into one another. Due to this design there results a very uniform force transmission from a gear wheel connected to the drive to the driven gear wheel. The vibration excitation of the gear wheels meshing with each other is thus reduced to a minimum.
An embodiment of the gearwheel mechanism is especially preferred where the distances of the transition between the straight line region and the arcuate region or the arcuate region and the involute measured from the end face of the gear tip are in an approximate ratio of 1:2 to one another. Due to this design a particularly uniform force transmission occurs in the vicinity of the tip of a tooth. This design insures that vibration excitations, which could result in noises inside the gearwheel mechanism, are at a minimum.
Furthermore an embodiment form of the gearwheel mechanism is particularly preferred, where the tooth profile or flank in the region of the tooth root is configured in the shape of a cycloid-like curve, especially a cycloid in order to avoid an undercut, which cycloid is directly adjacent to the involute provided in the central region of the tooth flank or profile. This results in an extension of the active tooth flank or profile which leads to a particularly uniform force transmission between the two associated gear wheels, which again assists in avoiding vibration excitations.